# get last known position of EOF
if (open(SEEK, "<seek") {
  $seek = <SEEK>;
  chomp $seek;
  close SEEK;
} else { # no EOF recorded, find it
  warn "Failed to read seek: $!\nCreating\n";
  open(LOG, "<$log") or die "Can't read $log: $!";
    # always a good idea to check the result of your open!
  seek(LOG, 0, 2);  # jump to the EOF
  $seek = tell(LOG);
  close LOG;
  &write_seek($seek);
  exit;
}

open(LOG, "<$log") or die "Can't read $log: $!";
seek(LOG, $seek, 0); # jump to the last EOF
while (<LOG>) {
  $id = (split / /)[2];
  $login_id{$id}++;
}
$seek = tell(LOG);
&write_seek($seek);
close LOG;

sub write_seek {
  my $seek = shift;

  open(SEEK, ">seek") or die "Can't write to seek: $!";
  print SEEK $seek;
  close SEEK;
}